Method of producing a tool for the non-cutting working of materials

ABSTRACT

IN THE METHOD OF PRODUCING TOOLS FOR THE NON-CUTTING WORKING OF MATERIALS, FOR EXAMPLE THE EXTRUSION OF METALS AND PLASTICS, WHEREBY THE WORKING SURFACES ARE SHAPED BY ELECTRO-EROSIVE TREATMENT, THE SURFACES ARE AFTERWARDS POLISHED ELECTROLYTICALLY.

United States Patent O US. Cl. 204-1295 1 Claim ABSTRACT OF THE DISCLOSURE In the method of producing tools for the non-cutting working of materials, for example the extrusion of metals and plastics, whereby the working surfaces are shaped by electro-erosive treatment, the surfaces are afterwards polished electrolytically.

Tools made of steel, for shaping of metals without cutting, for example by pressing or hammering, and for the extrusion of plastics, are often produced by electroerosive treatment to shape the working surface. In particular, in the dies for extrusion of metals and of plastics, the openings which determine the cross section are machined electro-erosively. The surfaces which arise exhibit a certain roughness, and must consequently be smoothed or polished by a final treatment by hand, since a rough surface would increase friction in the extrusion process in an inadmissible manner, and the surface finish of the extruded section would be affected. On the other hand, a hard surface layer arises during the electro-erosive treatment which hinders this final treatment. In filing by hand, for which purpose diamond files are necessary, the flat surfaces also easily become convex and thus are no longer technically at their best, for example as extrusion dies. The object underlying the invention is to remove these disadvantages in the manufacture by electro-erosive treatment of tools for the non-cutting working of materials. According to this invention the electro-erosively treated working surface of the tool is smoothed by electrolytic polishing, and the hard surface layer which arises during the electro-erosive treatment is removed.

The electrolytic polishing can be carried out in a simple manner and produces a high Surface finish. For this purpose the tool is immersed as an anode in an electrolyte and is treated with direct current. If the tool is a die, the cathode conveniently has the shape of the opening in the tool and is inserted into it.

Known electrode materials can be used for the cathode for the electrolytic polishing, for example graphite.

Advantageously the same electrode is used for electrolytic polishing as for the electro-erosive treatment. It is also advantageous to use cathodes of aluminium. These can easily be produced, by extrusion of a bar of aluminium, using the prototype of the tool to be made. This bar is then cut to the correct length and is etched to slightly reduce its size.

An electrolyte of methyl alcohol and nitric acid has been found to be particularly suitable. Other electrolyte compositions, known for the polishing of steel, may be used. They consist of perchloric acid-acetic acid mixture, or phosphoric acid, sulphuric acid, chromic acid and their mixtures.

EXAMPLE For producing a die for extrusion of sections of aluminium, the desired profile shape of the die opening is electro-erosively machined out of the die block. On the treated surface the hardness is increased, and reaches values of 640 up to 900 kp./mm. (Vickers hardness). The roughness amounts to about 25 to 30 m. For electrolytic polishing there is inserted into the die opening as cathode an aluminium bar which has been extruded with this die and etched for an hour in caustic soda. By the etching, the cross section of the bar is reduced to such an extent that it does not touch the die at any point. As electrolyte is used a mixture of 2 parts by volume methyl alcohol and 1 part by volume nitric acid. Polishing is carried out at room temperature for 9 minutes with direct current of about 5 amps.

After the polishing the hardness of the surface of the opening amounts to only 400 kp./mm. it has thus sunk again to the starting value before the electro-erosive treatment. The roughness amounts to 10 ,um. If this is not satisfactory it can be further reduced easily by simple polishing with emery, since the hard surface layer has been removed.

I claim:

1. A method of producing a tool having a working surface defining an opening,

comprising the steps of shaping a working surface of the tool by electro-erosion,

providing an outer hard layer surrounding the material of reduced hardness, the outer layer having a resulting surface, and

smoothing the resulting surface by electrolytic polishing until the hard surface layer is electrolytically removed,

using during the electrolytic polishing an electrode which consists essentially of aluminum and has a similar shape as the opening and is inserted into said opening, and has a contour sufficiently smaller in size compared to said opening tospace its external surface from the opening when inserted, said electrode being produced by extrusion through the opening after the electro-erosion and its contour being subsequently reduced in size by etching.

References Cited UNITED STATES PATENTS 3,275,543 9/1966 Williams 204--224 3,326,785 6/1967 Williams 204l40.5 2,382,549 "8/ 1945 Edmonson 204-1405 2,412,058 12/1946 Pfeil 204-l40.5 3,689,387 1972 Jumer 204l40.5 3,223,603 12 1965 Inoue 204143 2,516,105 7/ 1950 Mateosian 204--140.5

FOREIGN PATENTS 1,032,799 6/ 1966 Great Britain. 1,224,109 6/ 1960 France.

OTHER REFERENCES Electrolytic Polishing by J. S. Crout, Metal Industry, June 8, 1945, pp. 357-359.

A Survey of Solutions for Polishing Stainless Steel, Metal Progress, vol. 47 (1945), pp. 732-736.

B. Bartkiewicz: Werkstattstechnik (1964), pp. 196-4199.

G. K. Vandenburgh: Werkstattstechm'k (1963), pp.

THOMAS TUFARIELLO, Primary Examiner US. Cl. X.R. 204129.1 

